RFC 1763 PPP BVCP March 19951. Introduction
PPP has three main components:
1. A method for encapsulating multi-protocol datagrams.
2. A Link Control Protocol (LCP) for establishing, configuring,
and testing the data-link connection.
3. A family of Network Control Protocols for establishing and
configuring different network-layer protocols.
In order to establish communications over a point-to-point link, each
end of the PPP link must first send LCP packets to configure and test
the data link. After the link has been established and optional
facilities have been negotiated as needed by the LCP, PPP must send
BVCP packets to choose and configure the VINES network-layer
protocol. Once BVCP has reached the Opened state, VINES datagrams
can be sent over the link.
The link will remain configured for communications until explicit LCP
or BVCP packets close the link down, or until some external event
occurs (an inactivity timer expires or network administrator
intervention).
1.1. Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized.
MUST This word, or the adjective "required", means that the
definition is an absolute requirement of the specification.
MUST NOT This phrase means that the definition is an absolute
prohibition of the specification.
SHOULD This word, or the adjective "recommended", means that there
may exist valid reasons in particular circumstances to
ignore this item, but the full implications must be
understood and carefully weighed before choosing a
different course.
MAY This word, or the adjective "optional", means that this
item is one of an allowed set of alternatives. An
implementation which does not include this option MUST be
prepared to interoperate with another implementation which
does include the option.
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RFC 1763 PPP BVCP March 19951.2. Terminology
This document frequently uses the following terms:
datagram The unit of transmission in the network layer (such as IP).
A datagram may be encapsulated in one or more packets
passed to the data link layer.
frame The unit of transmission at the data link layer. A frame
may include a header and/or a trailer, along with some
number of units of data.
packet The basic unit of encapsulation, which is passed across the
interface between the network layer and the data link
layer. A packet is usually mapped to a frame; the
exceptions are when data link layer fragmentation is being
performed, or when multiple packets are incorporated into a
single frame.
peer The other end of the point-to-point link.
silently discard
This means the implementation discards the packet without
further processing. The implementation SHOULD provide the
capability of logging the error, including the contents of
the silently discarded packet, and SHOULD record the event
in a statistics counter.
2. A PPP Network Control Protocol for VINES
The Banyan VINES Control Protocol (BVCP) is responsible for
configuring, enabling, and disabling the VINES protocol modules on
both ends of the point-to-point link. BVCP uses the same packet
exchange mechanism as the Link Control Protocol. BVCP packets may
not be exchanged until PPP has reached the Network-Layer Protocol
phase. BVCP packets received before this phase is reached should be
silently discarded.
The Baynan VINES Control Protocol is exactly the same as the Link
Control Protocol [1] with the following exceptions:
Frame Modifications
The packet may utilize any modifications to the basic frame format
which have been negotiated during the Link Establishment phase.
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RFC 1763 PPP BVCP March 1995
Data Link Layer Protocol Field
Exactly one BVCP packet is encapsulated in the Information field
of a PPP Data Link Layer frame where the Protocol field indicates
type hex 8035 (Banyan VINES Control Protocol).
Code field
Only Codes 1 through 7 (Configure-Request, Configure-Ack,
Configure-Nak, Configure-Reject, Terminate-Request, Terminate-Ack
and Code-Reject) are used. Other Codes should be treated as
unrecognized and should result in Code-Rejects.
Timeouts
BVCP packets may not be exchanged until PPP has reached the
Network-Layer Protocol phase. An implementation should be
prepared to wait for Authentication and Link Quality Determination
to finish before timing out waiting for a Configure-Ack or other
response. It is suggested that an implementation give up only
after user intervention or a configurable amount of time.
Configuration Option Types
BVCP has a distinct set of Configuration Options.
2.1. Sending VINES Datagrams
Before any VINES datagrams may be communicated, PPP must reach the
Network-Layer Protocol phase, and the Banyan VINES Control Protocol
must reach the Opened state.
Exactly one VINES packet is encapsulated in the Information field of
a PPP Data Link Layer frame where the Protocol field indicates type
hex 0035 (Banyan VINES datagram). The maximum length of a VINES
datagram transmitted over a PPP link is the same as the maximum
length of the Information field of a PPP data link layer frame.
The format of the Information field itself is the same as that
defined in [2].
2.2. General Considerations
VINES supports an Address Resolution Protocol, VINES ARP, primarily
used for address assignment. Since this protocol is part of VINES
IP, it is fully supported over BVCP. VINES also supports a data-link
Echo Protocol (VINES Echo), used to test connectivity to a VINES
Server in a LAN environment, which is not supported over BVCP.
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RFC 1763 PPP BVCP March 19953. BVCP Configuration Options
BVCP Configuration Options allow modifications to the standard
characteristics of the network-layer protocol to be negotiated. If a
Configuration Option is not included in a Configure-Request packet,
the default value for that Configuration Option is assumed.
BVCP uses the same Configuration Option format defined for LCP [1],
with a separate set of Options.
Up-to-date values of the BVCP Option Type field are specified in the
most recent "Assigned Numbers" RFC [3]. Current values are assigned
as follows:
Value Option
1 BV-NS-RTP-Link-Type
2 BV-FRP
3 BV-RTP
4 BV-Suppress-Broadcast
Note: A suggestion was made to combine the BV-NS-RTP-Link-Type option
and the BV-RTP option into a single option that could negotiate one
of four settings (S-RTP, NS-RTP-LAN, NS-RTP-WAN, NO-RTP). This
suggestion has been rejected because VINES must already deal with a
mix of S-RTP and NS-RTP, and that pushing this information down to
the PPP layer is not desirable.
3.1. BV-NS-RTP-Link-Type
Description
This Configuration Option provides a way to negotiate the way the
Non-Sequenced Routing Update Protocol (NS-RTP) (pre-VINES 5.5,
i.e., 4.11 and 5.0) will run on the link. NS-RTP handles updates
differently depending on whether the interface is a LAN type or a
WAN type. For a LAN type, the full routing table is rebroadcast
every update interval (90 seconds). For a WAN type, the full
routing table is only transmitted for the first 3 update intervals
after the link comes up. After that only changes are transmitted
(for 5 update intervals). Note that this has no effect if
Sequenced RTP (VINES 5.5) is being used. More information on this
can be found in [2].
This option negotiates what an implementation is willing to
receive, and is negotiated separately per side of the PPP
connection. The acceptance of this option (by the peer) indicates
that the peer will send NS-RTP updates as if the link was a LAN
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RFC 1763 PPP BVCP March 1995
type. The rejection (or absence) of this option indicates that
the peer will send NS-RTP updates as if the link was a WAN type.
By default, NS-RTP updates are sent as if the link was a WAN type.
A summary of the BV-NS-RTP-Link-Type Configuration Option format is
shown below. The fields are transmitted from left to right.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1
Length
2
3.2. BV-FRP
Description
This Configuration Option provides a way to negotiate the use of
VINES Fragmentation Protocol (FRP). This protocol is used to
allow fragmentation and reassembly of a VINES packet over the
link. FRP prepends a two octet field to every packet going over
the link that contains a begin and end fragment information and a
sequence number. With PPP's default MRU of 1500, FRP is not
normally needed, and no FRP header would be sent with the VINES
packet. If a MRU of less than 1484 is negotiated, FRP will be
needed to send a full size VINES packet over the link. More
information on this can be found in [2].
This option negotiates what an implementation is willing to
receive, and is negotiated separately per side of the PPP
connection. The acceptance of this option (by the peer) indicates
that the peer will send VINES packets with a FRP header. The
rejection (or absence) of this option indicates that the peer will
send VINES packets without a FRP header.
By default, VINES packets are sent without a FRP header.
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RFC 1763 PPP BVCP March 1995
A summary of the BV-FRP Configuration Option format is shown below.
The fields are transmitted from left to right.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
2
Length
2
3.3. BV-RTP
Description
This Configuration Option provides a way to negotiate whether RTP
is used over the link. If dial-up lines with static routes are
being used, the use of RTP may be totally suppressed to conserve
bandwidth on the link.
This option negotiates what an implementation is willing to
receive, and is negotiated separately per side of the PPP
connection. The acceptance of this option (by the peer) indicates
that the peer will not send RTP packets. The rejection (or
absence) of this option indicates that the peer will send any RTP
packets.
By default, RTP packets are sent over the link.
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RFC 1763 PPP BVCP March 1995
A summary of the BV-RTP Configuration Option format is shown below.
The fields are transmitted from left to right.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
3
Length
2
3.4. BV-Suppress-Broadcast
Description
This Configuration Option provides a way to negotiate the sending
of VINES broadcast packets, i.e., packets with a destination VINES
network address of all ones. This option only affects VINES
packets that are not of type VINES ARP or VINES RTP. This option
can be used by a VINES Client to request that most of the
broadcast packets that would normally be sent to it by a VINES
Server be discarded, in order to conserve link bandwidth. Most of
the broadcast packets sent by a VINES Server are not useful to a
VINES Client.
This option negotiates what an implementation is willing to
receive, and is negotiated separately per side of the PPP
connection. The acceptance of this option (by the peer) indicates
that the peer MUST NOT send any VINES broadcast packets, other
than packets of type VINES ARP or VINES RTP. The rejection (or
absence) of this option indicates that the peer will send all
VINES broadcast packets.
By default, all VINES broadcast packets are sent.
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